Cancer of the colon is common in the western world and is an important cause of morbidity and mortality, having an incidence of about 5% in the U.S. population. As with other types of cancers, cancers of the gastrointestinal tract, including colon cancer, are characterized by abnormal development in cell proliferation and differentiation in the gastrointestinal tract.
The gastrointestinal tract, including the rectum and colon, is lined with epithelial cells which have a high proliferation rate. The lining of the colon, in particular, made up of columnar rows of epithelial cells, is characterized by a series of indentations or crypts. Epithelial cells in the bottom regions of the crypts proliferate and move upward toward the tops of the crypts. In the normal colon, the proliferation region of the large intestine normally occupies the basal or deeper three-quarters of the crypts. A relationship has been observed between the expansion of cell proliferation zones to the upper regions of the crypts and colon cancer. See M. Lipkin, "Biomarkers of Increased Susceptibility to Gastrointestinal Cancer: New Application to Studies of Cancer Prevention in Human Subjects," Cancer Research, Vol. 48, pp. 235-245 (Jan. 15, 1988).
More generally, neoplastic diseases are conditions in which abnormal proliferation of cells results in a mass of tissue called a neoplasm or tumor. Neoplasms have varying degrees of abnormalities in structure and behavior. Some neoplasms are benign while others are malignant or cancerous. An effective treatment of neoplastic disease would be considered a valuable contribution to the search for cancer preventive or curative procedures.
There has been an intensive search for chemoprotective agents for all individuals at risk for colon cancer and other gastrointestinal cancers, particularly individuals over the age of 45. One class of potentially therapeutically useful compounds are the non-steroidal antiinflammatory drugs ("NSAIDs"). NSAIDs, presently in common use as anti-inflammatory agents and as analgesics, are known to have neoplasia chemoprevention and other anti-neoplastic benefits. Physiologically, NSAIDs are known to inhibit the biosynthesis of prostaglandins by the inhibition of the cyclooxygenase enzyme which is ubiquitous in mammalian tissues. See Buckley et al., Drugs, 39(1):86-109 (1990). The role of NSAIDs in prevention of colorectal cancer is discussed in Heath et al., "Nonsteroidal Antiinflammatory Drugs and Human Cancer," Cancer, Vol. 74, No. 10, pp. 2885-2888 (Nov. 15, 1994).
However, the use of NSAIDs in colon cancer prevention has been associated with severe undesirable side effects, which include gastrointestinal, renal and hepatic toxicities, as well as increases in bleeding times due to disruption of platelet function (e.g., thrombocytopenia), and prolongation of gestation due to uterine effects. Another serious side effect associated with the use of certain NSAIDs is leukopenia (decreased white cell count in the blood), and consequent agranulocytosis.
Agranulocytosis is a life-threatening condition that develops very rapidly, and that is difficult to detect even with periodic white-cell counts. The leukopenia/agranulocytosis syndrome has been described for several NSAIDs, such as indomethacin, ketoprofen, and ibuprofen. Indeed, such NSAIDs are contraindicated in patients whose immune systems are compromised by HIV infection, chemotherapy, ionizing irradiation, corticosteroids, immunosuppressives, etc., or by such conditions as emphysema, bronchiectasis, diabetes mellitus, leukemia, burns and the like. A recent review of the adverse effects of NSAIDs is Borda et al., "NSAIDs: A Profile of Adverse Effects," Hanley and Belfus, Inc., Philadelphia, Pa., 1992.
The most recent epidemiologic survey showing that both aspirin and NSAIDs confer protection against colon cancer is Peleg, et al., "Aspirin and Nonsteroidal Anti-inflammatory Drug Use and the Risk of Subsequent Colorectal Cancer," Arch. Intern. Med., Vol. 154, pp. 394-400 (Feb. 28, 1994). This reference identifies a causal relationship between the use of NSAIDs, such as indomethacin, sulindac and peroxicam, and prevention of cancer of the large bowel and rectum. A risk benefit analysis is suggested, however, due to the severe potential gastrointestinal and renal side effects, particularly in the elderly.
The standard treatment for colon cancer currently consists of the administration of a known cancer fighting agent, 5-fluorouracil in combination with the antibiotic levamisole. No improvement in survival among colon cancer patients was shown when 5-fluorouracil was administered alone. The addition of levamisole, which is known to stimulate the immune system and increase T-cell count, showed improved survival rate among these patients. See Moertel et al., "Levamisole and Fluorouracil for Adjuvant Therapy of Resected Colon Carcinoma," N Engl J Med 1990; 322:352-358.
Many NSAIDs exhibit molecular chirality, and thus have R- and S-enantiomers. Such compounds typically are produced as racemic mixtures, which can subsequently be separated into the individual enantiomers.
The enantiomers of several 2-arylpropionic acid NSAIDs are discussed in Yamaguchi et al., Nippo Yakurigaku Zasshi, 90:295-302 (1987). Yamaguchi et al. state that the S-enantiomers of 2-arylpropionic acids have 15-300 times higher prostaglandin synthetase inhibitory activities than the R-enantiomers in the rat.
Caldwell et al., Biochem. Pharmacol. 37: 105-114 (1988) allege that "at best, the R-isomers of 2-arylpropionic acids! function as prodrugs for the therapeutically active S-forms" when the racemic drug is administered and thus add to both in the therapeutic and toxic effects of the active S-enantiomers. Caldwell et al. further contend that "at worst, the R-enantiomers are undesirable impurities in the active drug" causing difficulties due to non-stereoselective toxicity. The authors indicate that the use of the S-isomers alone should provide safer and more effective use of this class of drugs.
Similarly, it has been generalized that the pharmacokinetics of the enantiomers of 2-arylpropionic acids are different due, at least in part, to the unidirectional metabolic inversion of the R- to the S-enantiomer. However, it has been found that this interconversion depends on the particular compound and the particular species in which it is administered. Jamali, Eur. J. Drug Metabolism Pharmaco. 13: 1-9(1988).
Because of the toxicity and side effects previously described, many NSAIDs are no longer in use in human medicine as analgesics. Some of these NSAIDs include tiaprofenic acid, suprofen, carprofen, pirprofen and indoprofen.
A need has been identified for new formulations of NSAIDs that are effective in treating colorectal and other cancers but are more tolerable with regard to gastrointestinal toxicity. Thus, it would be particularly desirable to provide compositions and methods for the prevention of neoplasia and colorectal cancer but without the aforementioned disadvantages.